Whisk the mayonnaise, chili-garlic sauce, and vinegar together in a small bowl and set aside for the flavors to meld.

Adjust an oven rack to the middle position and heat the oven to 200 degrees. Set a wire rack inside a rimmed baking sheet. In a large bowl, whisk the cornstarch and cold water until smooth.

Bring 2 quarts of water, the salt, and the baking soda to a boil in a Dutch oven. Add the potatoes and return to a boil. Reduce the heat and simmer for 3 to 5 minutes, until the potato exteriors turn slightly mushy and starchy, though the centers should remain firm.

Whisk the cornstarch slurry to recombine it. Use a wire skimmer or slotted spoon to transfer the parboiled potatoes to the bowl with the slurry. Fold the potatoes gently with a rubber spatula until the liquid thickens into a light orange paste that clings heavily to the potatoes.

Heat the oil in a 12-inch nonstick skillet over high heat until it reaches 325 degrees—the oil should shimmer. Carefully add one-third of the potatoes. Fry until crisp and lightly browned, about 7 to 10 minutes, using tongs to flip them halfway through. Adjust the heat as needed to keep the oil between 280 and 300 degrees during the actual frying.

Transfer the fries to the prepared wire rack. If any stick together, use a fork to gently pry them apart. Season with salt and place the baking sheet in the oven to keep them warm while you return the oil to 325 degrees and repeat the process with the remaining batches. Serve hot with the spicy sauce.